So far, as the appearance of cumulative helium mass spectrometric combination leak detector (CHLD) employing the cryogenic pump technique with its test efficiency acceptable for requirements of the test on the sealability of electronic components, in many standards the test on a high rigour grade and a low equivalent standard leak rate L, employs the method of cumulative helium mass spectrometric gross-leak and fine-leak combination test. Current methods for cumulative helium mass spectrometric combination test all uses helium gas as tracer gas for gross-leak test, generally uses helium gas as tracer gas for fine-leak test, or may use various gas like argon gas, nitrogen gas, carbon dioxide, fluorocarbon compounds as tracer gas for fine-leak test. The sensitivity is higher when using helium gas as tracer gas for fine-leak test.
To control the helium leak rate background of the leak detector having test chamber, particularly to remove the leak rate of surficially absorbed helium of the component under test after helium pressurizing or helium prefilling so as to meet the requirements of being no larger than ⅕ or ⅓ of the criterion for helium measured leak rate of fine-leak test, a longer maximum test-waiting time after helium pressurizing or helium prefilling is needed. To quantitatively extend this maximum test-waiting time, the criterion for helium measured leak rate of gross-leak test should be correctly specified. Since the gross-leak test uses helium gas in the air as tracer gas, however the partial pressure of helium gas in air PHe0 is as low as 0.533 Pa, when the minimum detectable equivalent standard leak rate of gross-leak test L0 takes the value of 1 Pa·cm3/s as fluorocarbon-bubble method, the criterion for helium measured leak rate of gross-leak test R0max=1.42×10−5 Pa·cm3/s and the criterion for measured leak rate of fine-leak test Rmax must be less than R0max, which in some degree limits the range of cavity volume and the criterion for measure leak rate of fine-leak test adapted for cumulative helium mass spectrometric combination test. If increasing L0 and R0max, although in some degree the range of cavity volume and measured leak rate adapted for fine-leak test in combination test is expanded, the maximum test-waiting time determined by L0 gets shorter, and therefore the time for removing surficially absorbed helium of the component under test gets shorter. In a larger cavity volume range, the removal of the absorbed leak rate cannot meet the test requirement of the criterion for measured leak rate of fine-leak test. Accordingly for the current cumulative helium mass spectrometric combination test, there forms a unbreakable dilemma between making a stricter criterion for measured leak rate of fine-leak test as well as expanding the cavity volume range adapted for combination test, and extending maximum test-waiting time as well as removing absorbed helium of the component under test.
Based on the above description, it is necessary to seek for a test method to make gross-leak and fine-leak combination test using the cumulative helium mass spectrometric leak detector more practicable and to lengthens maximum test-waiting time of fine-leak test on a precondition of making a stricter criterion for measured leak rate of fine-leak test, which makes the removal of the leak rate of absorbed helium meet the test requirements of a stricter criterion and expends the adapted range of cavity volume and criterion for measured leak rate of fine-leak test.
Since the partial pressure of argon gas in the air is 946 Pa, much larger than the partial pressure of helium gas PHe0, when internal helium gas and argon gas are equivalent to the air, the leak rate of argon gas is 562 times as that of helium gas for the same gross-leak aperture, so that the sensitivity of using argon gas as tracer gas of gross-leak test is higher and in a dry environment the leak rate of surficially absorbed argon of the component under test can meet the test requirements of a lower L0. Accordingly it is able to select a lower minimum detectable equivalent standard leak rate L0 for gross-leak test, thereby extending the maximum test-waiting time of fine-leak test, which can remove absorbed argon and helium gas more sufficiently and meet the test condition requirements of criterions for gross-leak and fine-leak test. Using argon gas as gross-leak tracer gas, the values of helium measured leak rate of fine-leak test of the component under test after gross-leak test can effectively indicate the sizes of fine-leak, which is unnecessary to be limited by that the criterion Rmax for measured leak rate for fine leak must be smaller than the criterion R0max for measured leak rate for gross-leak as using helium gas as tracer gas, and able to effectively expand the range of cavity volume and criterion for measured leak rate for fine leak adapted for combination test, thus allowing cumulative helium mass spectrometric combination test to have more practicability and applicability.